In some kinds of gas combustion type driving tools, combustible gas is injected into a combustion chamber sealed within a body, then mixed gas of the combustible gas and the air is stirred within the combustion chamber, and the mixed gas thus stirred is burnt within the combustion chamber to generate high-pressure combustion gas within the combustion chamber. The high-pressure combustion gas acts on a striking piston accommodated within a striking cylinder to impulsively drive the striking piston within the striking cylinder. A nail supplied to a nose portion beneath the body is driven into a steel plate or concrete by a driver coupled to the lower surface side of the striking piston. Such the combustion-gas driven driving machine is formed as a portable tool in a manner that a vessel such as a gas container filed with the combustible gas is attached within the tool and a battery acting as a power source for igniting the combustible gas is attached to the tool. Thus, the combustion-gas driven driving machine can perform the driving procedure of a nail or a pin without being restricted by a source of drive such as electric power or compressed air.
The aforesaid gas combustion type driving tool is provided with a feed mechanism for sequentially feeding connected fasteners accommodated within a magazine to a nose portion. As the feed mechanism, there is known one which is configured in a manner that the connected fasteners configured by coupling many fasters in a straight manner are accommodated within a sheath-shaped magazine, the connected fasteners are always pressed toward the nose portion side by a constant output spring, whereby immediately after a fastener supplied to an injection port within the nose portion is driven, a next fastener is supplied within the nose portion.
However, since such the straight magazines is small in the number of fastener to be accommodated therein, it is required to attach a cylindrical magazine which can house therein connected fasteners configured by coupling many fasters wound in a coil manner.
The feed piston cylinder mechanism is generally used as a feed mechanism of a fastener in the cylindrical magazine. The feed piston cylinder mechanism is configured in a manner that a feed piston accommodated within a feed cylinder so as to be slidable freely is provided with a feed claw which engages with and disengages from the connected fasteners accommodated within the magazine and the feed claw is reciprocally moved to a nail feed direction for feeding the feed claw to the nose portion side and to an evacuation direction in opposite thereto.
Thus, the cylindrical magazine together can be employed together with the feed piston cylinder mechanism. In this case, it is considered that the feed piston of the feed piston cylinder mechanism can be moved reciprocally by utilizing the pressures of a spring and the combustion gas within the combustion chamber. That is, the feed piston is fed by the spring and evacuated by the gas pressure.
However, according to the structure where the combustion chamber is directly coupled to the feed cylinder via a gas tube, the combustion gas almost simultaneously acts on the striking piston and the feed piston (feed claw). Thus, the feed piston starts the evacuation operation almost simultaneously with the striking operation of the striking piston and so a fastener becomes unstable at the time of the driving operation. That is, when the feed piston remains at the feed position by the spring, a nail at the head position supplied within the nose portion is pressed by the feed claw, whereby the posture of the fastener is stable. The posture of the fastener is preferably stable while the fastener is driven by the driver. However, when a striking mechanism operates by the pressure of the combustion gas, if the feed piston evacuates simultaneously with that the driver is driven together with the striking piston thereby to drive the fastener, a force for pressing and holding the fastener is lost and so the posture of the fastener becomes unstable. As a result, the fastener can not be surely driven with a correct posture.
Thus, in a nailing machine disclosed in JP-U-05-072380, as a means for delaying the operating timing of a feed piston, a check valve is provided at the pre-stage of a feed mechanism, whereby the gas pressure at the pre-stage of the feed piston is held and the sealing control of a gas tube is performed by an exhaust valve interlocked with a contact arm.
However, according to the aforesaid method, the exhaust valve for releasing the check valve is required and it is difficult to secure the sealing property of the valve in an environment where dust etc. likely adheres to the tip end of the nose portion.